Re: [PATCH v2 for 5.4 3/4] media: hantro: Fix motion vectors usage condition

[Tomasz Figa]

Hi Jonas,

On Tue, Oct 8, 2019 at 3:33 AM Jonas Karlman <jonas@xxxxxxxxx> wrote:
>
> On 2019-10-07 19:45, Ezequiel Garcia wrote:
> > From: Francois Buergisser <fbuergisser@xxxxxxxxxxxx>
> >
> > The setting of the motion vectors usage and the setting of motion
> > vectors address are currently done under different conditions.
> >
> > When decoding pre-recorded videos, this results of leaving the motion
> > vectors address unset, resulting in faulty memory accesses. Fix it
> > by using the same condition everywhere, which matches the profiles
> > that support motion vectors.
>
> This does not fully match hantro sdk:
>
>   enable direct MV writing and POC tables for high/main streams.
>   enable it also for any "baseline" stream which have main/high tools enabled.
>
>   (sps->profile_idc > 66 && sps->constrained_set0_flag == 0) ||
>   sps->frame_mbs_only_flag != 1 ||
>   sps->chroma_format_idc != 1 ||
>   sps->scaling_matrix_present_flag != 0 ||
>   pps->entropy_coding_mode_flag != 0 ||
>   pps->weighted_pred_flag != 0 ||
>   pps->weighted_bi_pred_idc != 0 ||
>   pps->transform8x8_flag != 0 ||
>   pps->scaling_matrix_present_flag != 0

Thanks for double checking this. I can confirm that it's what Hantro
SDK does indeed.

However, would a stream with sps->profile_idc <= 66 and those other
conditions met be still a compliant stream?

>
> Above check is used when DIR_MV_BASE should be written.
> And WRITE_MVS_E is set to nal_ref_idc != 0 when above is true.
>
> I think it may be safer to always set DIR_MV_BASE and keep the existing nal_ref_idc check for WRITE_MVS_E.

That might have a performance penalty or some other side effects,
though. Otherwise Hantro SDK wouldn't have enable it conditionally.

> (That is what I did in my "media: hantro: H264 fixes and improvements" series, v2 is incoming)
> Or have you found any video that is having issues in such case?

We've been running the code with sps->profile_idc > 66 in production
for 4 years and haven't seen any reports of a stream that wasn't
decoded correctly.

If we decide to go with a different behavior, I'd suggest thoroughly
verifying the behavior on a big number of streams, including some
performance measurements.

Best regards,
Tomasz

>
> Regards,
> Jonas
>
> >
> > Fixes: dea0a82f3d22 ("media: hantro: Add support for H264 decoding on G1")
> > Signed-off-by: Francois Buergisser <fbuergisser@xxxxxxxxxxxx>
> > Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
> > ---
> > v2:
> > * New patch.
> >
> >  drivers/staging/media/hantro/hantro_g1_h264_dec.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/staging/media/hantro/hantro_g1_h264_dec.c b/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> > index 7ab534936843..c92460407613 100644
> > --- a/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> > +++ b/drivers/staging/media/hantro/hantro_g1_h264_dec.c
> > @@ -35,7 +35,7 @@ static void set_params(struct hantro_ctx *ctx)
> >       if (sps->flags & V4L2_H264_SPS_FLAG_MB_ADAPTIVE_FRAME_FIELD)
> >               reg |= G1_REG_DEC_CTRL0_SEQ_MBAFF_E;
> >       reg |= G1_REG_DEC_CTRL0_PICORD_COUNT_E;
> > -     if (dec_param->nal_ref_idc)
> > +     if (sps->profile_idc > 66)
> >               reg |= G1_REG_DEC_CTRL0_WRITE_MVS_E;
> >
> >       if (!(sps->flags & V4L2_H264_SPS_FLAG_FRAME_MBS_ONLY) &&
>